An 11-year-old Brooklyn girl with a severe case of swine flu was among the three latest victims to succumb to the virus in New York — raising the city’s total to 15, more than half the death toll recorded nationwide.

In a letter to parents of kids at the Urban Assembly School for Criminal Justice in Borough Park, Principal Mariela Graham said the girl, who was not identified, died Sunday.

Teachers-union President Randi Weingarten, testifying at a City Council hearing on swine flu earlier yesterday, said that the child had underlying conditions and that the flu diagnosis was determined after an autopsy.

“She was healthy the last time I saw her,” said one parent.

Meanwhile, the WHO declared a swine-flu pandemic yesterday, with more than 28,000 cases worldwide and 144 deaths; WHO chief Dr. Margaret Chan described the virus as “now unstoppable.”